Radio-frequency (RF) platforms are high-volume products, which include several integrated circuits (ICs) for audio, power management, radio transceiver, etc. ICs can offer the best economical figures for mass-production products, since the mask costs are fixed which leads to decreasing unit costs as the number of fabricated ICs increases.
The over-the-air (OTA) performance defines the capabilities of the RF platform. OTA performance is an important selling factor and can be a crucial selection criterion for a potential customer, as well as the unit cost. OTA performance is a function of antenna performance and capabilities of RFIC and baseband ICs. Typically, the size of the antenna scales inversely to the RF frequency, i.e. antennas become larger when the wavelength increases. Within the user equipment (UE), the size of the antennas is limited due to a small form-factor product thus leading to sub-optimal antenna performance. Therefore, the platform performance can be degraded at frequencies below 1 GHz leading to decreased uplink/downlink performance.
State-of-the-art RFICs are designed to operate at several different bands, for example Global System for Mobile Communications (GSM) 850, 900, 1800, and/or 1900, Wideband Code Division Multiple Access (WCDMA), High Speed Packet Access (HSPA) and/or Long Term Evolution (LTE) Bands 1, 2, 3, etc. Typically, there is an RF filter (or duplex filter in the case of links utilising Frequency Division Duplexing (FDD)) placed between the antenna and RFIC to filter out unwanted radio signals. Due to different uplink/downlink configurations, there are several bands where the RF filter has considerable insertion loss (IL). The larger the IL is, the less sensitive (higher noise figure) the receiver will be. For example, WCDMA and LTE Bands 2 and 3 have a narrow duplex frequency gap, (the frequency difference between the highest transmission frequency and the lowest receiver frequency) resulting in a higher IL. Since the receiver sensitivity in the abovementioned bands is comparatively worse, the range of the wireless link is shorter. As a result, the network design becomes more challenging and more expensive, for example more base stations are needed.
Therefore, from a network operators' perspective, a good reference sensitivity level is a relevant figure-of-merit. In the near future, the IL before the Low Noise Amplifier (LNA) stage of an RF receiver is expected to increase due to inter-band carrier aggregation (CA) as more complex front-end module (FEM) designs are required. Furthermore, some of the existing bands will be extended to cover even wider bandwidths and probably with narrower duplex distances (e.g. Band 2+G-block, Uplink: 1910-1915 MHz, Downlink: 1990-1995 MHz). In such cases, additional losses are expected due to diplexer and switch losses, and additional filtering required due to challenging duplex and co-existence scenarios. More generally, there is a need for cost-optimisation, including in relation to filter modules and materials.
The LNA is usually the first amplifying stage in an RF receiver. According to Friis' equation, the LNA sets the minimum noise figure of the receiver. A low LNA noise figure is a crucial parameter determining the reference sensitivity level of the whole transceiver or RF platform. The LNA is also a crucial part for determining the input impedance of the RFIC. Sufficient input matching performance is required because the performance of the RF filter preceding the LNA will degrade if the input of the LNA is not properly matched to a certain input impedance. Since the RF filters preceding the LNA typically have a fixed frequency range, the RFIC inputs will be matched to specific frequencies as well. Depending on the LNA structure, there might be a need to utilize off-chip matching components to set the input matching to the desired level. Depending on the number of RFIC inputs, the count of the external matching components can become high thus being an expensive and bulky solution.
RFIC performance is a crucial factor in determining the radio platform performance. Within the RFIC, it is the LNA which defines the minimum possible noise figure, which in part defines the reference sensitivity level. The sensitivity performance and input matching configurability of RFICs are fixed and this leads to sub-optimal platform design, since there are several levels of customer (for example network operators, Original Equipment Manufacturers (OEMS), etc.) and different mobile device products each of which may have different requirements for the same chipset. Since the cost of individual ICs scales down when the number of units increases, it is not economically wise to design separately optimised ICs for different customers and/or products.
From the above it can be seen that there are a number of different design factors to be considered when designing an RFIC, and that accommodating some or all of these factors simultaneously can prove difficult. There is therefore a need to enhance RFIC design by providing design adaptivity including improved ways of accommodating various design factors.